topic 4.1.1/2 - 4.2.1/2 micropara

• Virions


  Complete virus particles, very small and simple in structure

  
• Viruses


  • Most range in size from 10 to 300 nm in diameter, although some can be up to 1µm in length
  • The smallest virus is about the size of the large hemoglobin molecule of a red blood cell

  
• Electron microscopes were invented, allowing the first photographs of viruses to be obtained


  1930s
• First photographs of viruses were obtained

  1940
• Negative staining procedure coupled with TEM revolutionized the study of viruses

  1959
• Organisms that viruses infect

  • Humans
  • Animals
  • Plants
  • Fungi
  • Protozoa
  • Algae
  • Bacterial cells
• Bacteriophages


  • T2
• Viruses


  • Possess either DNA or RNA
  • Unable to replicate on their own, replication is directed by the viral nucleic acid once it has been introduced into a host cell
  • Do not divide by binary fission, mitosis or meiosis
  • Lack the genes and enzymes necessary for energy production
  • Depend on the ribosomes, enzymes and metabolites of the host cell for protein and nucleic acid production
• Characteristics used to classify viruses

  • Type of genetic material (DNA or RNA)
  • Whether the virus nucleic acid is single stranded or double stranded
  • Whether the virus nucleic acid is positive-sense or negative-sense
  • Shape of the capsids
  • Number of capsomeres
  • Size of capsid
  • Presence or absence of an envelope
  • Type of host that it infects
  • Type of diseases it produces
  • Target cell
  • Immunologic or antigenic properties

  
• Categories of viruses based on genome type

  • Double-stranded DNA
  • Single-stranded RNA
  • Single-stranded DNA
  • Double-stranded RNA

  
• Theories on the origin of viruses

  • Coevolution Theory
  • Retrograde Evolution Theory
  • Escaped Gene Theory
• Animal Viruses


  • May consist solely of nucleic acid surrounded by a protein coat or they maybe more complex, e.g. enveloped or containing enzymes that play a role in viral multiplications within host cells
• Steps of animal virus multiplication

  1. Attachment

  2. Penetration

  3. Uncoating

  4. Biosynthesis

  5. Assembly

  6. Release
• Viruses need to destroy the host cell in order to escape and repeat the cycle over again
• Inclusion Bodies


  Remnants or collection of viruses, often seen in infected cells and used as a diagnostic tool to identify certain viral diseases

  
• Latent virus infections


  Viral infections where the virus remains dormant in the host, but can be reactivated by triggers like fever, stress or sunlight
• Oncogenic Viruses or Oncoviruses


  Viruses that cause cancer
• Oncogenic Viruses


  • Epstein-Barr virus
  • Certain types of DNA Viruses (Nasopharyngeal carcinoma, Burkitt lymphoma, Human papillomaviruses)
  • Certain types of RNA Viruses (T-lymphotropic Virus type 1, HIV)

  
• Human Immunodeficiency Virus (HIV)


  A lentivirus that causes AIDS, it has an enzyme called reverse transcriptase that allows its RNA genome to be replicated into proviral DNA

  
• Proviruses


  The viral genome that is integrated into the host cell genome, allowing the virus to cause latent infections and avoid immune responses
• Ebola virus


  A thread-shaped virus that causes hemorrhagic fever, thought to have crossed over from bats
• Zika virus


  Transmitted by mosquitoes and responsible for a large number of birth defects
• Antiviral Agents


  Drugs used to treat viral infections, they interfere with viral replication by disrupting critical phases or inhibiting synthesis of viral components
• Bacteriophages


  Viruses that infect bacteria, they are obligate intracellular pathogens that must enter a bacterial cell to replicate
• Types of Bacteriophages


  • Icosahedron Bacteriophages
  • Filamentous Bacteriophages
  • Complex Bacteriophages
• Bacteriophage genome types


  • Single-stranded DNA phages
  • Double-stranded DNA phages
  • Single-stranded RNA phages
  • Double-stranded RNA phages
• Virulent Bacteriophages


  Always cause the lytic cycle in bacterial cells
• Temperate Bacteriophages


  Do not immediately initiate the lytic cycle unlike virulent phages
• Steps in the multiplication of bacteriophages

  1. Attachment

  2. Penetration

  3. Biosynthesis

  4. Assembly

  5. Release
• Mimivirus


  An extremely large double-stranded DNA virus that was recovered from amoebas, it is so large it can be observed using a compound microscope and has a genome larger than some bacteria

  
• Pandoravirus


  The largest discovered giant virus, almost twice as large as Mimivirus and capable of encoding over 2,000 genes

  
• Plant Viruses


  More than 1,000 different viruses that cause plant diseases, usually transmitted via insects, mites, nematodes, infected seeds, cuttings, tubers and contaminated tools
• Plant Virus


  • Bean Yellow Mosaic Virus
• Viroids


  Small, naked fragments of single stranded RNA that can interfere with plant cell metabolism and stunt/kill plants
• Prions


  Small infectious proteins that cause fatal neurological diseases in animals and humans, where the brain becomes riddled with holes
• Phenotypic categories of bacteria

  • Gram-negative and have cell wall
  • Gram-positive and have cell wall
  • Those that lack cell wall
• Identifying bacteria

  1. Establish numerical taxonomy systems

  2. Compare composition of genetic material

  3. Identify by physical characteristics
• Characteristics used to identify bacteria

  • Cell shape and morphologic arrangement
  • Staining reactions
  • Motility
  • Colony morphology
  • Atmospheric requirements
  • Nutritional requirements
  • Biochemical and metabolic activities
  • Specific enzymes the organism produces
  • Pathogenicity
  • Genetic composition

  
• Gram Reaction

  Gram-positive or Gram-negative
• Cell Morphology

  The study of the forms of things